The present invention relates to a three-stage coupling arrangement for an electrical data exchange system including first, second and third stages, each stage comprising a plurality of coupling matrixes each of which has inputs and outputs and a matrix of switching points for selectively switching through signals from the inputs to respective outputs; and intermediate conductors for connecting the outputs of the coupling matrixes of one stage with the inputs of the coupling matrixes of a next stage; wherein the inputs of the coupling matrixes of the first stage constitute the inputs of the coupling arrangement and the outputs of the coupling matrixes of the third stage constitute the outputs of the coupling arrangement.
Coupling arrangements are used to selectively connect signal sources with signal drains. There are single-stage coupling arrangements and multi-stage coupling arrangements. A three-stage coupling arrangement is disclosed in an article by Charles Clos, entitled, "A Study of Non-Blocking Switching Networks", in the The Bell System Technical Journal, Volume XXXII 1953, pages 406-424.
The coupling arrangement shown in FIG. 2 of that article has a first stage, stage (a), a second stage, stage (b), and a third stage, stage (c). Each stage is composed of a plurality of coupling matrixes. The coupling matrixes of one stage differ in the number of their inputs and outputs from those of the other stages. For example, the coupling matrix of the first stage has six inputs and eleven outputs, the coupling matrix of the second stage has six inputs and six outputs and the coupling matrix of the third stage has eleven inputs and six outputs. Thus, three different embodiments of coupling matrixes are required. The number of embodiments is reduced to two if the switching points employ switching means which permit signal transmission in both directions, as is the case, for example, for metal contacts. In such a case, the embodiment provided for the first stage can also be used for the third stage with the inputs and outputs exchanged.
This coupling arrangement is non-blocking. That is, for every possible combination of already existing connections between a signal source and a signal drain every additional connection which is appropriate merely on the basis of the still available inputs and outputs can indeed be switched through. This is possible without a requirement for so called "recoupling" also called "rearrangement".